Inorganic films possess much higher thermoelectric performance than their organic counterparts, but their poor flexibilities limit their practical applications. Here, Sb2Te3/Tex hybrid thin films with high thermoelectric performance and flexibility, fabricated via a novel directional thermal diffusion reaction growth method are reported. The directional thermal diffusion enables rationally tuning the Te content in Sb2Te3, which optimizes the carrier density and leads to a significantly enhanced power factor of >20 µW cm–1 K–2, confirmed by both first‐principles calculations and experiments; while dense boundaries between Te and Sb2Te3 nanophases, contribute to the low thermal conductivity of ≈0.86 W m–1 K–1, both induce a high ZT of ≈1 in (Sb2Te3)(Te)1.5 at 453 K, ranking as the top value among the reported flexible films. Besides, thin films also exhibit extraordinary flexibility. A rationally designed flexible device composed of (Sb2Te3)(Te)1.5 thin films as p‐type legs and Bi2Te3 thin films as n‐type legs shows a high power density of >280 µW cm–2 at a temperature difference of 20 K, indicating a great potential for sustainably charging low‐power electronics. A high ZT of ≈1 at 453 K is achieved in an inorganic Sb2Te3/Te hybrid thin film via a novel directional thermal diffusion reaction growth method with extraordinary flexibility, and the rationally designed flexible device shows a high power density by a low‐temperature difference.